The invention is directed to electric range heater assemblies which conventionally incorporate a tubular heating element and a support or support spider affixed to the heating element for support thereof and manipulation of the assembly as a unit. The assembly will normally also incorporate a connector or grounding bracket engaged between the terminal legs of the heating element with the connector stabilizing the legs relative to each other and preventing shifting of the relatively more flexibly mounted outer leg, that is the leg associated with the outer convolution of the heating element.
At present, two basic heater assemblies are or have been commonly used. In the first assembly, the support or spider is staked directly to the convolutions of the central heating portion of the heating element in at least two places. This staking is basically affected by forming the support, or more particularly selected ones of the support arms, with upwardly projecting integral ear-like extensions which receive a portion of the tube therebetween and are subsequently deformed thereagainst or thereover. In some instances, the tube itself may be preformed at the point of staking to provide an improved profile for accommodation of the staking operation. Such a staking arrangement for the securement of a support to a heating element will be noted at the left-hand portion of FIG. 2 of the patent to R. E. Sand, U.S. Pat. No. 3,021,414. Other than for this illustration, the patent appears to make no reference to this relatively common manner of interconnecting a support to an overlying heating element.
While the staking procedure is widely used, it does give rise to several problems. For example, in order to achieve maximum holding strength, the extending portions of the support, those portions which are to be deformed or staked to the tubes, must reach well above the central plane of the tube to effect a positive retention. However, a restraining design consideration is that the extended portion of the support cannot project above the planar top surface of the tube after staking as this would prevent cooking vessels from sitting flat on the heater surface. The preforming of the tube at the point of staking, as previously referred to, is an attempt to improve the strength and consistency of the staking operation. However, this is an expensive procedure and can itself result in unacceptable disruptions in the tube.
Even in those circumstances wherein all of the appropriate staking dimensions are maintained within specifications, the force of actually deforming the support extensions into the tube often results in an upward "ballooning" of the planar top surface of the tube. Similarly, slight variations in the support spider, and in particular the positioning of the staking extensions, can result in deformations of the heater tube, and in particular the convoluted central heating portion.
Even under situations wherein the staking operation is mechanically correct, there is an inherent problem due to the disruption of the magnesium oxide inside the heater tube which results from each staking operation. This disruption tends to create a section in the heater with reduced heat transfer ability. This in turn can lead to premature failing of the heater.
Finally, the intimate contact, provided by the staking operation, between the support spider and the heater tube gives rise to an increased tendency for heat drain from the tube to the spider. This in turn decreases the efficiency of the heater and results in an uneven heat pattern.
The second conventionally used manner of attaching the support to the formed heater tube is through the use of a formed tie bracket or strap. Note for example the member 16 in the patent to L. S. Kozbelt et al., U.S. Pat. No. 3,350,674. Such a bracket, while overcoming many of the problems associated with a staking operation, gives rise to its own set of problems.
For example, the use of a welded bracket is costly both in material and labor. The welding of a tie bracket to a thin wall tube tends to result in a high level of scrap due to "blow holes." Further, the weld must be made through an oxide layer or the oxide must be removed by a separate brushing operation. Finally, the use of such tie brackets does not provide a firm assembly between the support and the formed tube, an anti-rattle device normally being utilized.
The Kozbelt et al. patent is also of interest in illustrating the connector or ground bracket, as widely utilized. This connector, designated by reference numeral 19, is provided with two apertures therethrough which receive the two terminal heater element legs. The connector is rigidly secured to the inside leg by an integrally formed boss or ring surrounding the corresponding aperture and crimped to the inside leg. The relatively more flexibly mounted outside leg is positioned against excessive longitudinal inward movement by a second ring or boss which is in the nature of a "break-away" member retained on the connector by small readily severed sections which break or part from the connector upon a crimping of this ring to the outside terminal leg. In this manner, the ring prevents longitudinal inward movement of the outside terminal leg, resisting any tendency for such movement upon a plugging-in of the heater assembly, and at the same time provides for an accommodation of movement through expansion and contraction during the various heating and cooling cycles. The "break-away" ring, thus provided, is a constant source of production line and tool problems due to the critical nature of the connection between the ring and the connector or ground bracket itself.
The patent to Drugmand et al., U.S. Pat. No. 3,644,710, is of interest in illustrating a heater assembly incorporating both a connector with a break-away boss or ring, and strap-like members which are welded to the convolutions and depend therefrom for engagement with the spider support.